The current invention is a system for holding an object in mid-air under the influence of fixed and variable magnetic forces countering the gravitational pull on the object.
Such systems can be used for display purposes such as advertising or commercial displays; and/or educational purposes such as spinning globes.
It is perceived that the larger the gap between the suspended object and the structure containing the magnets and control systems, the more desirable the device becomes.
Such a systems has been disclosed in U.S. Pat. No. 6,154,353 whereby a fixed support has an upper station containing a permanent magnet, an electromagnet and a sensor system. The suspended object also has a permanent magnet and floats, below the upper station of the support frame. The permanent magnets are configured so as to attract one another in an upwards direction, countering the downwards gravitational force on the object. Hence a theoretical balance point is defined whereby in the absence of any external influences or fluctuations in the magnetic and gravitational forces, the object would be held steady in mid-air.
In fact, such a balance point is virtually impossible to maintain and so control systems are applied, disclosed for example in DE 4210741, whereby fluctuations in the field provided by the permanent magnet in the object, are interpreted, and consequently the current to the electromagnet in the support frame is adjusted to provide an attractive or repelling force in order to prevent the object moving away from the balance point.
U.S. Pat. No. 6,154,353 discloses such a system modified by the fact that the permanent magnets provide an attractive upwards force slightly greater than the downwards force on the object due to gravity. In this case the electromagnet is normally employed to provide a small repelling force to provide a fine balance and establish what might be called a dynamic balance point.
In the dynamic balance point the object is balanced in mid air by an upward force provided by the attraction of the permanent magnets countered by the forces of gravity plus the repelling force of the electromagnet acting on the permanent magnet in the object.
If the object moves away from the dynamic balance point, stationary sensors detect the change in the field caused by the positional variation of the permanent magnet in the object. If the field rises above a predetermined level the current to the electromagnet is increased and the repelling force consequently increases to push the object downwards. By extension, if the field falls below a certain value the current in the electromagnet is decreased such that the repelling force is reduced and the object is pulled upwards.
The advantages of this system are that relatively small amounts of power are needed to achieve the fine balancing provided by the electromagnet. Furthermore if the power fails the object will move upwards towards the frame rather than downwards. However, the gap between the object and the structure is less than is theoretically possible.